1. Field of the Invention
This invention relates to a method and a device for implementing the method that tracks the optimal maximum power point in a system that supplies power from a direct-current power source, such as that generated by a solar cell array (photovoltaic generator), etc., which has a bow-shaped current-voltage characteristic, to a load via a switching converter so that the output power of the direct-current power source is maximized with respect to changes, etc., in the direct-current power source characteristic by controlling the operating point of the switching converter. The solar cell array (photovoltaic generator) shown above is hereinafter referred to simply as a solar cell.
2. Description of the Prior Art
A prior art method that controls the power point (operation point) so that the power generated by the solar cell is maximized measures the voltage and current of the solar cell, performs an analog-digital conversion of those values and then digitally calculates the product of the voltage and current, or calculates the product of the voltage and current by analog computation, and then varies the duty ratio of the switching converter connected to the solar cell so that this product is maximized.
There is also known a method that monitors the output of the switching converter and varies the duty ratio of the switching converter so that the voltage or current of the output is maximized. Another method that is generally used measures the temperature of the solar panel and controls the power point using that temperature as a function of the temperature.
However, the control circuits in the above methods that measure the voltage and current of the solar cell and calculate their product are complicated and expensive. There is also a problem with quantization error in the analog-digital conversion. Further, the method that monitors the output of the switching converter is severely affected by fluctuation in the load. In the method that controls by measuring the temperature, etc., control shifts far from the optimal power point due to the inconsistency of the temperature of the solar panel or the intensity of sunlight or wind to which it is subjected, and it is necessary to attach a sensor and wire it for measuring the temperature, etc.
The purpose of this invention is to provide an inexpensive tracking method and device that do not require a temperature measurement sensor, are not affected by inconsistencies in the state of the solar panel or fluctuations in the load, and are capable of accurately tracking the power point so that the power generated by the solar cell is maximized.